It is necessary in certain types of laboratory analysis work to accurately measure pressure changes, volume changes and fluid flow in a high fluid pressure system. In fine core analyses conducted in the oil industry, for example, the system pressures are commonly in the order of 10,000 psi, while the changes in pressure, volume and flow which must be measured are very small. Pressure changes are measured to a fraction of a psi, volume changes are measured in thousandths of a cc and flow changes are measured in thousandths of a cc per minute.
Valves currently available suffer from one or more problems. In most cases the internal volume of the valve changes upon opening and closing of the valve. In other words, the structure of the movable component of the valve increases or decreases the volume of the flow path through the valve depending upon whether the valve is open or closed. As a result, the pressure of the fluid and the total volume in the system changes. Since extremely small changes in pressure and volume can be significant, even small changes in the volume of the system can cause erroneous readings, leading to erroneous conclusions about the core sample.
In addition, most valves available for use in such systems do not give flexibility of operation when incorporated in a multiple valve. In a three-way valve, for example, it can be desirable to be able to close both outlets or open them both, which is not possible with currently available valves. Further, most valves used in such systems are quite expensive.
It would therefore be desirable, in the measurement of small fluctuations in pressure, volume and flow in a high pressure fluid system, to use a valve that maintains a constant internal volume so as not to produce false pressure readings. It would also be desirable that such a valve be economical and capable of a full range of settings when used in a multi-valve arrangement.